The present invention relates to a plasma processing method of etching a silicon-containing object to be processed such as a silicon substrate with a plasma.
In a process of manufacturing a silicon substrate for a semiconductor device, the substrate is thinned during a thinning process. This thinning process is performed, subsequently to forming of a circuit pattern on the surface of the silicon substrate, by mechanically polishing a back side opposite to the circuit-formed side. The mechanical polishing forms a damaged layer including a micro-crack at the surface of the silicon substrate. To prevent strength of the silicon substrate from decreasing due to this damaged layer, etching is performed to remove the damaged layer after the mechanical polishing. As this etching, plasma etching is utilized instead of conventional wet etching using a chemical solution.
To achieve a higher etching rate, this plasma etching directed to silicon, gas including carbon tetrafluoride gas is used as plasma-generating gas. The carbon tetrafluoride gas is ionized or excited by a plasma discharge to form an ion and a radical, which etches the silicon surface.
In the plasma etching using the carbon tetrafluoride, a carbon-containing film, that is, a compound of fluorine and carbon, which is a product generated in a reaction caused by the plasma processing of the silicon surface, re-adheres to a portion of the silicon surface. This re-adhering compound prevents the plasma etching from being performed, reduces an overall etching rate, varies plasma etching effect depending upon the degree of the re-adhesion. Consequently, the etched surface has a hazy appearance and hence has reduced visual quality.
An exemplary embodiment of the presently claimed invention is a method of plasma-processing a silicon-containing object at a high etching rate while generating no hazy appearance on the surface of the object, thereby to have excellent visual quality.
This plasma-processing method includes mounting the object to be processed on a mounting unit disposed within a process chamber, generating a plasma by feeding plasma-generating gas including sulfur hexafluoride and helium into the process chamber and causing a plasma discharge, and etching the object with the generated plasma.